The present invention relates to a method and apparatus for coupling ultrasound and laser energy to an optical fiber combined with irrigation/aspiration for therapeutic purposes directed to and within a cataractous lens. With minor modification this invention can be adapted to treat other tissues within the human body.
For many years optical fibers have been utilized in the medical industry to transmit light (laser energy) to targets for diagnostic as well as therapeutic purposes. Every eye is divided into an anterior and posterior chamber. When the lens becomes cloudy for any of a variety of reasons sight is impaired and the cloudy lens must be removed. This clouding of the lens is termed xe2x80x9ccataractxe2x80x9d. Following removal of the lens, an intraocular lens (IOL) implant can be placed in the posterior chamber of the eye to replace the focusing function of the human lens. Alternatives to intraocular lens implants are thick spectacle eyeglasses or contact lenses to focus the light.
A number of techniques are now in use for this common surgical procedure. An incision, typically 3 mm can be made in the eye surface and a metal tipped ultrasonic probe is inserted to a position adjacent to the lens. The ultrasonic energy then fragments the lens material, which can then be removed by irrigation and aspiration.
Laser radiation is now widely used in various surgical techniques, particularly those involving the eye. For example, Krasnov U.S. Pat. No. 3,971,382 describes a technique in which laser radiation is focused onto the anterior capsule of the lens to form a hole through which the cataract substance can be drawn from the lens capsule.
Optical fibers are also commonly used for medical and other applications to transmit coherent radiation from a laser to some other location in the body where material is to be disintegrated or coagulated. U.S. Patent application Ser. No. 702,569 filed Feb. 19, 1985 describes a micro instrument with an optical fiber. The optical fiber can be inserted into the eye for removal of abnormal tissue such as tumors. Bath U.S. Pat. No. 4,744,360 describes a fiber-optic laser device for removing cataractous lenses. Coherent radiation with wavelengths between 193 nanometers and 3000 nanometers is said to be effective.
However, a problem with laser based systems is that there is the potential for explosions in the eye. Bath U.S. Pat. No. 4,744,360 teaches how to avoid explosions in the eye by first determining the ablation threshold and carefully configuring the laser parameters to deliver laser pulses to approximate the ablation threshold. Bath first determined the ablation threshold for human cataractous lenses to be approximately 0.5 J/cm2and published her results in Archives of Ophthalmology in 1987(volume 105, page 1164, 1987). The laser surgical parameters of energy density, power density, pulse duration, repetition rate and at a specific wavelength must be configured for optimal surgical effectiveness and safety. The teachings of Bath U.S. Pat. No. 4,744,360 and of the fundamentals of fiberoptic laser cataract surgery have spawned a plethora of devices and methods (referenced herein) for fiberoptic laser cataract surgery which is often referred to as laserphaco, i.e. laser phaco.
As above mentioned, it is known to use ultrasonic energy to disintegrate cataracts within the eye. This technique is known as phacoemulsification and was pioneered by Kelman. The phacoemulsification technique is limited because a metal tip associated with the technique becomes very hot at high frequencies, thereby potentially damaging the eye. Thus current practice has been to avoid performing the phacoemulsification procedure on xe2x80x9chard cataract nucleixe2x80x9d due to this heat problem, as well as the other technical difficulties associated with phacoemulsification.
The more dense cataract nucleus would require higher vibrational frequencies or increased phacoemulsification times thereby increasing the risk of heat related complications. Heat is produced at the target site of the vibratory motion, i.e. the cataractous lens, due, in part, to friction. This is a well known complication of ultrasonic processes and was recognized as early as 1967 as discussed by Delaney (vida infra, U.S. Pat. No. 3,352,303) who discusses xe2x80x9cthe problems associated with heat from wave (i.e. vibrational) energy . . . .xe2x80x9d
The original and current phacoemulsification devices feature a metal cutting member which vibrates at high frequencies which is applied in direct contact with the cataractous lens.
This metal rod cutting member has been likened to a miniature xe2x80x9cjack hammerxe2x80x9d. Significantly, in the art of reference related to ultrasound cataract surgery, the cutting member has always been fabricated of metal. The ultrasonic vibration of metal cutting members results in a finite percentage of heat related surgical complications such as xe2x80x9cthermal wound injuryxe2x80x9d.
In a special supplement to the Feb. 15, 1998 issue of Ocular Surgery News, there was an article written by Dr. Paul Ernest entitled xe2x80x9cThermal Wound Injury During Phacoemulsificationxe2x80x9d (pg.25-27). In this article, the occurrence of thermal wound injury was directly attributed to delays in irrigation and high phacoemulsification power settings. This publication is significant because the primary source of the xe2x80x9cheatxe2x80x9d problem, still goes unrecognized even in 1998. This reference also documents that the problem is also unsolved. The applicant""s present invention addresses and solves this problem.
In summary, what is needed is a cataract removal system that does not have the heat problems associated with the phacoemulsification process and also is not susceptible to the explosions generated by laser based systems. The present invention addresses such a need. The present invention uses a non-metal optical fiber to delivery the combination of both laser energy and ultrasound energy to cataractous lenses in a safe and effective methodology.
The present invention relates to a method and apparatus in which pulsed ultrasound and laser energy are transmitted by means of an optical fiber delivery system to the lens of the eye for therapeutic purposes including cataract surgery. Combined laser and ultrasound energy are transmitted by a flexible line containing at least an optical fiber surrounded in part by an irrigation sleeve through a limbal incision on the eye surface, preferably 1 mm or less. A capsulotomy is made and the flexible line is advanced to a position immediately in contact with the crystalline lens. Ultrasound energy is delivered to the lens in pulsed doses. The vibrational frequencies are chosen based on the hardness of the lens nucleus in the specific surgical case. Vibrational frequencies are chosen to optimally cause processes of sonofragmentation, sonodisruption, sonocavitation of the lens nucleus. The placement of the irrigation sleeve to surround the fiberoptic results in cooling of the vibrational member. The circulation of irrigating fluid at and near the tip of the fiber also facilitates heat loss. Based on the knowledge of the ablation threshold for human lenses the parameters of the laser radiation are selected for transmission and delivery through the optical fiber. Laser parameters such as energy density, power density, pulse duration, repetition rate and wavelength are chosen to optimize processes of photophaco-ablation, photophaco-fragmentation, photophaco-disruption, photophaco-decomposition. The propagation of ultrasound energy down a non-metal line for cataract surgery is novel in the art of cataract surgery. Another novel feature of Applicants"" invention is the reduction of heat generated by ultrasonic vibratory mechanisms. This unexpected result is obtained because of the novel design and processes enabled by the continuous flow of irrigating fluids about the fiber optic. The use of a fiber-optic line for the dual transmission of ultrasound energy and laser energy for the purpose of fragmenting cataractous lenses is a second novel discovery demonstrated by applicant""s invention.
The ultrasound and laser processes fragment the cataractous lens into extremely small particles less than 1 mm in diameter. These fragmented particles and lens cortex can be irrigated and aspirated from the capsular bag via an aspiration sleeve which is formed about and extending along the irrigation sleeve.
Since the particles produced by the laser and ultrasound processes are extremely small, the device can be made extremely small and therefore the surgical incision site can be made smaller. Smaller surgical incisions have the advantage of faster healing and more rapid visual rehabilitation. Utilizing an optical fiber further permits the energy to be more effectively and efficiently focused onto the lens to be removed.
The present invention employs an optical fiber which allows high frequency probe output without the high temperatures associated with conventional ultrasound probes for removing cataracts. In summary, the present invention exploits the advantage of utilizing an optical fiber to precisely deliver units of energy to loci within the lens. Moreover, the unique anatomy and biomechanical architecture of the lens lends itself to mechanical disruption resulting from photoacoustic and/or sonic processes.